I'd take it to a tailor. One of the best things you get out of a tailor is not the alteration, but an informed second opinion as to what needs doing. My tailors so honest he quite often says "it's your imagination, the fit is fine as it is", rather than charge me for an alteration.

Ask what he thinks, and whether it's worth upsizing. For what it's worth, you should feel a bit of a tug around the shoulders the first time you put it on. It's a good sign the jacket fits.

1. If a jacket doesn't fit around the shoulders it's the wrong size, no matter how well it fits anywhere else. Fit on the shoulders is everything. Changing this is major work and will likely affect the way the entire jacket hangs. It's usually not worth the risk of having it tailored.

2. A jacket should NOT tug or wrinkle or anything else at the shoulders the first time you wear it. It's not a good sign at all that it's a good fit. It's a sign that the jacket is too small.

I said you should feel a pleasant hug around your shoulders when you first put it on, not that the jacket should wrinkle. A lot of men misidentify this as being too tight, when actually it's just a good, slim fit.

I say if you have an experienced tailor who you know well and trust, ask his opinion. Or post a picture.

Ok thanks fellas, think I will go to the store and try the size up if they have it. Its a real pain in the ass ill have to make a special journey to the next city some 30 miles away to get to a shop. Online returns just take to long.

I'm doing a lot of fitness at the moment and have dropped 1 or 2 pounds so I'm worried that as soon ad that wait goes back on its gonna be too snug.

What a shit.

No consistency in sizing at all every other reiss garment I own is small and fits like a glove.

May I ask which blazer you have bought? the fit on a lot of Reiss blazers will vary slightly because of they way they are cut and the amount of padding/canvas they put into it. A lot of the casual blazers such as the Irving/Manor are relatively slim fitting and have an awful lot of structural material put into them so they tend to be a bit tighter, more restrictive and rigid. They also have quite high armholes (I have found when I tried them when they came into store) which can often feel a bit too tight and uncomfortable.

I'm tempted to say that the tugging is probably more from the construction and the higher armholes (does it pull around the back of the armpit and the skirt?) usually I would just say get it taken out a tiny bit at the back just to relieve the pressure. You can only take an inch out on Reiss blazers anyway so it wouldn't affect the overall cut that much. However, this does rely on the shoulders fitting right. It's hard to tell without seeing exactly where it is pulling, I've had a couple of chaps in recently and the drape is good, it is just the tiniest bit too small and it pulls slightly under the arms; i've had those let out a bit to give the extra room. It sounds a bit like construction is giving you a few issues rather than the actual fit of the jacket itself, they're so rigid that it can feel like it doesn't fit quite right. I was quite shocked by how stiff some of them were.

To avoid any costly mistakes I would go and try the size up, an arse I know but if you ring the store first you can check the availability, if they don't have one they might be able to order one in but because Reiss has just gone on sale I'm not sure they will want to transfer the stock, it would take between a week and 10 days to come in if they did.

If the 42 is way too big on the shoulders then it might be worth chatting to the sales assistant in store or to a tailor about it and asking if you can get it taken out just a touch, you won't want much let out, just enough to relax the fit. Reiss should do the alterations for you.

Anyone would think you work for Reiss, boom tish! (I'm here all night)

I spoke to the manager in the bristol store and he recons against taking out the material apparently it will leave "scarring", if I go size up they will do "dart" the sides and that should do the trick so im told